The present invention is related to the field of fiberoptic network laser sources and, more particularly, to laser diode sources having very high spectral stability.
In many fields of optics, such as precision optical instruments, optical telemetry (remote) sensing systems, high performance optical sensors and the like, laser sources having a high degree of spectral stability are very desirable. With such sources, the wavelength (or frequency) of the laser light output varies little with changing conditions. Perhaps the field with the most pressing need, at least in terms of numbers, for a laser source with a stable spectral output is the Dense WDM (DWDM) fiberoptic network.
In WDM (Wavelength Division Multiplexed) networks, the wavelength of an optical signal is used to direct the signal from its source to its destination. Each network user typically has a laser source operating at a specific wavelength which is different from those of other laser sources. Hence a stable laser source having a fixed output wavelength is desirable. As the number of users on a WDM network increases, a larger number of laser sources are required for signal generation. The large bandwidth networks, such as DWDM networks, increase the demand for highly stabilized laser sources.
To increase the bandwidth and the number of communication channels in WDM networks, the ITU, the International Telecommunications Union, has proposed the Dense WDM, or DWDM. The separation between communication channels in the DWDM is only 0.8 nm, or 100 GHz in frequency. Thus a light source for such a network must also have a very narrow output linewidth, i.e., the wavelength of the output signal must be concentrated in a very narrow portion of the optical spectrum, and the wavelength of the source must be extremely stable to avoid drifting into the wavelength range of another channel.
In present laser sources, such as DFB (Distributed Feedback), DBR (Distributed Bragg Reflectors) or Fabry-Perot laser diode laser sources, the output wavelength changes in varying degrees with changes in the bias current of the laser diode and changes in temperature. FIG. 1, for instance, illustrates the changes in spectral output in response to changes in the bias current for a modern DFB laser diode. Various techniques are used to stabilize the bias current and temperature of the laser diode. However, conventional bias current and temperature stabilization are inadequate for the stringent requirements for many optical systems, such as DWDM networks.
The present invention provides for such a laser source with an output which is very stable.